This invention generally relates to a seal assembly, and more particularly to an intershaft seal assembly for a rotational assembly.
Conventional mechanical seal assemblies are used in rotating equipment to provide a seal between regions of high and low fluid pressure and temperature. For example, seal assemblies are used to seal a rotating shaft on a pump, compressor, agitator, gas turbine, or other rotating equipment.
Gas turbine engine type rotational assemblies typically include (in serial flow communication) a fan section, a compressor section, a combustor section, and a turbine section. During operation, air is pressurized in the compressor section and mixed with fuel in the combustor section for generating hot combustion gases. The hot combustion gases flow through the turbine section which extracts energy from the hot combustion gases. In a multiple spool type gas turbine engine, a rotor assembly includes a high speed shaft and a low speed shaft that power the engine components using the energy extracted from the hot combustion gases.
In gas turbine engines, mechanical seal assemblies are used to prevent hot, high pressure air from entering a bearing compartment that operates at a low pressure and temperature. For example, a front bearing compartment in a multiple spool gas turbine engine is filled with an oil mist to lubricate the bearings that support the high speed rotor shaft and the low speed rotor shaft. The high speed rotor shaft and the low speed rotor shaft are separated by a gap filled with working medium gas. The working medium gas cools the rotor shaft. An intershaft seal assembly prevents the working medium gas from leaking into the oil compartment and prevents the oil mist from leaking out of the bearing compartment into the gap. The intershaft seal assembly typically includes two axially offset graphitic carbon ring mechanical face seals that seal the gap between the high speed rotor shaft and the low speed rotor shaft. Secondary seals may also be provided between the two face seals to limit leakage between the face seals.
Modern day advanced gas turbine engine programs typically include rotor shafts that operate at different speeds and have different sealing requirements. In some cases, the difference between the rotational speeds of a high speed rotor shaft and a low speed rotor may be relatively significant. The speed variations experienced by each face seal may result in unbalanced sealing between the high and low speed rotor shafts. Disadvantageously, known intershaft seal assemblies have not adequately provided for the different speed and sealing requirements of the rotor shafts. Additionally, intershaft seal assemblies are typically heavy, complex and expensive to produce, repair and replace.
Accordingly, it is desirable to provide a dual configuration intershaft seal assembly for a rotational assembly having rotor shafts including different sealing requirements that reduces seal assembly design space, reduces cost and reduces the overall weight of the rotational assembly.